1. Field of the Invention
This invention relates generally to a method for predicting mechanical properties of rocks using the mineral compositions of the rocks which are provided by in-situ logging tools.
2. Brief Description of Related Art
Formations in the earth are characterized by stress conditions which vary with depth and whose principal directions are generally vertical and horizontal. In the horizontal plane at any point, the horizontal stress reaches a maximum in one direction and a minimum at right angles to the maximum condition. Information concerning these maximum and minimum horizontal stress conditions is of substantial value in a variety of disciplines such as underground transportation systems, foundations of major structures, cavities for storage of liquids, gases or solids, and in prediction of earthquakes. Further, this information is essential in petroleum exploration and production, e.g., while drilling a well or borehole the information is useful for blowout prevention, in a completed well it is useful for evaluating hydraulic fracture treatment, and also in determining many critically important aspects of reservoir behavior, such as bulk and pore volume compressibility, permeability, direction of fluid flow, and reservoir compaction/surface subsidence.
Mechanical properties of formation rocks include stiffness coefficients, Young's modulus in an isotropic plane, Young's modulus in direction normal to the isotropic plane, Poisson's ratio in the isotropic plane, Poisson's ratio in a direction normal to the isotropic plane, and shear modulus. Such intrinsic rock properties are important pieces of information needed to properly interpret and model in-situ reservoir behavior.
Traditional techniques for determining rock properties include analysis of core samples. This involves the need to obtain and bring the core samples to the surface which can be a costly operation. To this end, a need exists for an improved method for predicting mechanical properties of rocks using the mineral compositions of the rocks ascertained from in-situ logging tools. It is to such a method that the present invention is directed.